Radiopaque polyurethane resin compositions

ABSTRACT

Radiopaque compositions are provided by formulating polyurethane resins, alone, or combined with vinyl resins, with alkyl or alkoxyalkyl 2,5-diiodobenzoates, 2,3,4,6-tetraiodobenzoates or mixtures thereof. The compositions are useful in the manufacture of X-ray opaque medical devices, particularly medical surgical tubing. Surgical tubing with excellent plastic memory is provided, well adapted to forming flares and curved tips necessary for selective renal and celial arteriography. Multi-wall and co-tapered multiwall tubing constructions are also disclosed.

This application is a division of Ser. No. 40,278, filed May 18, 1979,now U.S. Pat. No. 4,250,072, which in turn is a continuation-in-part ofcopending application Ser. No. 862,773, filed Dec. 21, 1977, nowabandoned, which in turn is a continuation of application Ser. No.712,189, filed Aug. 6, 1976, now abandoned.

This invention relates to novel radiopaque resin compositions and shapedarticles prepared therefrom. More particularly, the invention pertainsto compositions of polyurethane resins, alone, or in combination withvinyl resins, and polyiodobenzoic acid esters and their use inmedical-surgical devices.

BACKGROUND OF THE INVENTION

Archer and Flynn, U.S. Pat. No. 3,361,700, disclose that a family ofalkoxyalkyl esters of diiodobenzoic acid are radiopaque and suitable toplasticize vinyl resins into a form useful to manufacture tubings forcatheters and similar products. Flynn, U.S. Pat. No. 3,645,955 disclosesthat di- and tetraiodoesters used alone or in combination with thealkoxyalkyl diiodoesters are superior for this purpose because they showless tendency to exude and lower concentrations provide a better balancebetween flexibility and stiffness. In the copending application ofFlynn, Ser. No. 862,773, there are described certain multi-wall tubingconstructions, with a passing mention of polyurethane as a material ofconstruction, but no suggestion is made that this be combined with anyradiopacifier, especially the iodoesters mentioned above. Burlis et al,U.S. Pat. No. 3,752,617 disclose methods for making multiwall tubing,co-tapered along its length, but use plastics other than polyurethane,and make no mention of any additives, specifically by name, to producedifferent X-ray sensitive characteristics. The foregoing patents andapplication are all incorporated herein by reference.

While the iodoester opacified vinyl resin compositions are quitesuitable for the production of tubing of simple types useful forintubation sets and catheter needles, they are not completelysatisfactory for production of shaped devices. For example, if flared,or if formed into curved tips, the shapes tend to revert to straighttubing--a so-called loss of plastic memory effect. It has now been foundthat if the vinyl resin is replaced partially or completely by athermoplastic polyurethane, the iodoester radiopacified compositions areamenable to the induction of complex shapes--and they'll stay that way.Such tubings provide catheters eminently suitable for selective renalarteriography and for celial arteriography, and also for the manufactureof pig-tail catheters. Surprisingly, the iodoesters do not show the sametendency to overplasticize the urethane esters as they do the vinylesters, and, moreover, there is lesser need to use a radioparentplasticizer with urethanes and, in fact, it is preferred to omit aradioparent plasticizer completely. As will be shown, the newcompositions lend themselves well to the formation of highlyadvantageous multi-wall tubing constructions. In one feature of theinvention, a thin, inner core of iodoester-radiopacified polyurethaneand a thicker outer core of plasticized vinyl resin eliminatesextraction problems with fluids passing through the core. In anotherfeature, an inner core of nylon or polypropylene will provide an outerjacket of iodoester radiopacified urethane or urethane-vinyl withstiffness, but much less tendency to kink in a multiwall construction;and such tubes are also easily manufactured in a co-tapered wallthickness construction in which the variations in twisting resistanceprovide enhanced ease of insertion through torturous body passages.

In summary, optically clear radiopaque formulations based onthermoplastic polyurethane (TPU) according to this invention have thefollowing distinct advantages over vinyl (PVC)-based compositions of theprior art:

(i) ease and flexibility in formulation and processing: In contrast toPVC formulations, TPU does not require a primary plasticizer or heatstabilizer. PVC-based systems, in general, are temperature and shearsensitive, and consequently, the melt processing range is ratherlimited.

(ii) potentially less toxic: PVC is more susceptible to thermal/shearinduced degradation. In plasticized PVC formulations, both theplasticizer and the residual monomer are subject to migration andextraction phenomena. (The newer grades of PVC, admittedly, containinsignificant quantity of residual monomer). In recent years, PVC hascome under increased public scrutiny and criticism.

(iii) physical and functional properties: TPU can be formulated toobtain a much broader range of physical properties, if desired. Distinctadvantages of TPU formulations will be in higher tensile strength,elongation and excellent abrasion resistance and tear strength, andespecially in retention of plastic memory.

(iv) better blood compatibility: In many tests, the thrombo-resistanceof TPU has been shown to be superior to PVC.

(v) better ability to accept heparinization.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the accompanyingdrawings in which:

FIG. 1 is a longitudinal view of a catheter made from one form of thetubing made in accordance with the present invention and wherein, forillustrative purposes, the distal end is tapered and shaped to form a"J" tip, and the proximal end is flared;

FIG. 2 is an enlarged cross-sectional view of radiopaque tubingaccording to this invention;

FIG. 3 is an elongated cross-sectional view of tubing having aradiopaque inner core and a transparent outer shell;

FIG. 4 is an enlarged cross-sectional view of tubing having atransparent core and a radiopaque outer shell; and

FIG. 5 is an enlarged, fragmentary cross-sectional view along thelongitudinal axis of an embodiment tube of this invention having atransparent co-tapered core and a radiopaque, correspondingly co-taperedjacket, extruded as in FIG. 6.

DESCRIPTION OF THE INVENTION

In accordance with the present invention, there are provided radiopaquecomposition comprising

(a) a resin which includes from 100 to 33 parts by weight of athermoplastic polyurethane and from 0 to 67 parts of a polymer orcopolymer of a halogenated vinyl monomer; and

(b) a radiopacifier therefor consisting of a diiodobenzoate or atetraiodobenzoate of the formula ##STR1## wherein R¹ is hydrogen oriodo, R is alkyl or alkoxyalkyl and a mixture of said compounds, saidradiopacifier (b) comprising 10 to 40 parts by weight per 100 parts byweight of (a) and (b).

Preferably each R¹ is iodo and R is (lower)alkyl or (lower)alkoxy(lower)alkyl. The most preferred radiopacifiers are n-butyl2,3,4,6-tetraiodobenzoate, 2-ethoxyethyl 2,5-diiodobenzoate, or amixture thereof.

The thermoplastic polyurethanes are known to those skilled in this art.They are described in the Encyclopedia of Polymer Science andTechnology, Vol. 11, pages 506-563, New York, Interscience Publishers,1969, and especially on page 549. They are also commercially availablefrom a number of suppliers, such as Hooker, as Rucothenes, especially3713, and from Upjohn, as Pellethene 75D, from Mobay, as Texin, and fromUniroyal, as Roylar.

Suitable vinyl resins are described in the abovementioned U.S. Pat. No.3,645,955. They are available from a number of sources, such asEscambia, Nos. 3225, 3250 and 3255; Diamond No. 450 and No. 500; Borden,106PM and Dow Chemical Co., 100-4.

The radiopacifier compounds (b) can be made by procedures fullydescribed in the above mentioned U.S. Pat. Nos. 3,645,955 and 3,361,700.In general, a 2,3,4,6-tetraiodobenzoyl halide or 2,5-diiodobenzoylhalide will be treated with an alkanol or alkoxyalkanol at ordinarytemperatures, preferably in the presence of an acid acceptor.Alternatively, the free acid can be reacted with a sodium alkoxide oralkoxyalkoxide. The product can be recovered and purified in a known waye.g., distillation

When used in the appended claims, the term "alkyl" contemplates straightand branched chain radicals of from 1 to 30 carbon atoms, and the term"(lower)alkyl" contemplates such groups of from 1 to 6 carbon atoms.

The term "radioparent" plasticizer means a conventional plasticizer, forexample, a dialkyl ester of aromatic or aliphatic polybasic acids, e.g.,dioctyl adipate, which is commercially available from Rohm & Haas Co.,as Monoplex DIOA. Also contemplated are epoxy plasticizers, such asSwift & Co.'s Epoxol 9-5. The term "heat stabilizer for said vinylresin" embraces metallic salts, based on tin, calcium, zinc and thelike. A suitable commercial heat stabilizer is based on calcium andzinc, available from Advance Division of Carlisle Chemical Works, asCZ-11C.

The formulations will be aided in some cases by the inclusion oflubricants such as metallic stearate, stearic acid, paraffin wax,mineral oil, etc., in conventional amounts. See U.S. Pat. No. 3,645,955,incorporated herein to minimize unnecessarily detailed description.

The compositions are prepared and converted into useful products bytechniques well known to those skilled in the art.

In one manner of proceeding, the fluid ingredients, e.g., radiopaquecompound(s) if liquid, are blended with the powdered solids, e.g.,thermoplastic polyurethane resin and, optional, vinyl resin, stabilizersand plasticizers and then fused and mixed under pressure, e.g., in aBanbury-type mixer and discharged. Conventional 2-roll compoundingtechniques can also be used. The composition is cooled and granulated.

If extrusions are to be made, the granulated composition can be fed to aconventional machine, for example, a 30 millimeter Reifenhauser-typesingle screw extruder operated at suitable temperature, e.g., 280°-330°F. and the tubing or other shapes formed at a suitable rate, e.g.,7,000-10,000 feet per hour and cut automatically to length.

As is pointed out above, the compositions of this invention can be usedfor many various and diverse purposes, e.g., protective sheeting,surgeon's gloves, intubation sets, heart catheters, stomach tubes, nasaltubes, thoracic catheters and the like. The following examples primarilyillustrate the use of these compositions in the form of single andmultiple wall surgical tubing. However, from the foregoing descriptionand the following examples and by reference to other well knownteachings, the methods and modes by which the plasticized radiopaqueurethane resin compositions of this invention can be formed into variousother articles will be readily apparent to those skilled in the art.

The medical grade radiopaque tubing prepared as described in thefollowing examples is non-toxic, non-reactive to tissue and may besterilized by gas or cold sterilization solutions. The tubing isgenerally dispensed as such and the surgeon or trained technician willform it into catheters for roentgenography. For maximum convenience, thetubing can also be preformed into articles and dispensed, e.g., assterile disposable intravenous catheters.

By way of illustration, catheters according to this invention will befabricated from the medical-surgical tubing of the following examples byoperations comprising tip forming, tip finishing, shaping, side holeforming, and flaring. Before use they will be sterilized.

Those skilled in the art will prepare a variety of tip shapes. Forinternal mammary and axillary artery branches a three-quarter loop isformed in the distal end. For precutaneous arteriography and cerebralarteriography via femoral, a 45°-60° smooth bend will be formed in thedistal end. Selective renal arteriography and celiac arteriographyrequires a one-half loop. Hepatic venography uses about a seven-eighthsloop. For trans-septal left-heart catheterization via the femoral vein,a three-quarter loop, like that above-described for mammary branches,but larger, is formed. On the other hand, abdominal aortography viabrachial artery uses a rather large, one-third closed loop and thoracicaortography via the femoral artery uses the same shape but bigger. Forlumbar aortography via the femoral artery the tip is straight out. Forcoronary arteriography, the end of the catheter is looped.

The heavier-walled tubing is formed into such typical shapes byinserting a forming wire within the tubing and heating in a tiny flameuntil visibly softened. By pulling from both ends the tubing is drawn tothe wire and forms a uniform lumen around it. The tip is formed bycutting, e.g., with a razor blade, at the drawn diameter and is smoothlyrounded in the flame. Next a precurved wire is inserted into the tubewhich is then immersed in hot water until the tubing softens. Quenchingin cold water will cause the catheter to conform to the curve of theforming wire. Side hole or eye punching is accomplished by rotating asharpened hole punch cannula under slight pressure. The holes should belarge enough to expel contrast media without excess build up ofinjection pressures but should be no larger than 2/3 of the internaldiameter of the tubing. The catheter is cut to the preselected lengthand flared. Heating in a small flame and rotating on a flaring toolproduces a flare of the desired size. The catheter can be bonded at theflare, e.g., with epoxy cement, to a suitable hub. On the other hand, anadapter can be used to screw the catheter to a Luer-Lok stopcock, or thelike.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following non-limiting examples illustrate the present invention.

EXAMPLES 1-5

    ______________________________________                                        Example           1      2      3    4    5                                   ______________________________________                                        Composition (parts by weight)                                                 Resin,                                                                        thermoplastic polyurethane,                                                   Hooker Rucothane 3713                                                                           1800   36.23  67.47                                                                              66.66                                                                              --                                  Resin,                                                                        thermoplastic polyurethane                                                    Roylar 65N Uniroyal                                                                             --     36.23  --   --   66.6                                n-Butyl 2,3,4,6-tetraiodobenzoate                                                                500   27.52  32.53                                                                              33.33                                                                              33.33                               ______________________________________                                    

The compositions are mixed in a Banbury mixer for 4 minutes at 345° F.and for 2 minutes at 310° F., discharged, and granulated through a 1/8in. screen. The granulated products are extruded in a 30 mm.Reifenhauser screw extruder at 310°-330° F. into medical-surgical singlewall tubing of the type shown in FIG. 2, 0.065 O.D. X 0.044 I.D.--wall0.0105", having properties eminently suitable for use as intubation setsand in catheter needles.

EXAMPLES 6-10

The procedure of Example 1 is repeated, partially or completelyreplacing the 2,3,4,6-tetraiodo compound with a 2,5-diiodoester.

    ______________________________________                                                          6      7      8    9    10                                  ______________________________________                                        Composition (parts by weight)                                                 Resin,                                                                        thermoplastic polyurethane,                                                   Royalr 65N, Uniroyal                                                                            66.66  69.02  67.8 --   --                                  Resin,                                                                        thermoplastic polyurethane                                                    Rucothene 3713    --     --     --   66.66                                                                              66.66                               n-Butyl 2,3,4,6-tetraiodobenzyl                                                                 --     15.70  26.5 --   16.67                               2-Ethoxyethyl 2,5-diiodobenzoate                                                                33.33  15.70   7.5 33.33                                                                              16.67                               ______________________________________                                    

Thin wall tubings extruded from these compositions are clear and usefulfor making catheters.

EXAMPLES 11-15

The procedure of Example 1 is repeated, effecting partial replacement ofthe polyurethane with vinyl resin in the following formulations

    ______________________________________                                        Example           11     12     13   14   15                                  ______________________________________                                        Composition (parts by weight)                                                 Resin, thermoplastic poly-                                                    urethane Rucothene 3713                                                                         --     46.25  48.12                                                                              33.75                                                                              23.12                               Resin, thermoplastic poly-                                                    urethane Rucothene 363                                                                          25.00  --     --   --   --                                  Resin, polyvinyl chloride,                                                    Goodyear BK 80    43.73  21.86  27.18                                                                              32.50                                                                              43.23                               n-Butyl 2,3,4,6-tetra-                                                        iodobenzoate      12.36  22.43  11.21                                                                              16.25                                                                              11.21                               2-ethoxyethyl 2,5-diodo-                                                      benzoate          12.99  6.49   10.74                                                                              15.00                                                                              18.24                               Epoxy plasticizer,                                                            Epoxol 9-5        5.12   2.56   2.28 2.00 3.28                                Calcium zinc stabilizer,                                                      CZllC             0.78   0.39   0.45 0.5  0.69                                ______________________________________                                    

Flexible tubings having utility in intubation sets are obtained.

EXAMPLE 16

The procedure of Example 1 is repeated, but the extruded tubing has anouter diameter of 0.098 inch and an inside diameter of 0.054 inch. Thisis formed into a finished catheter as illustrated in FIG. 1. Tubing 10tapers down to a main body section 11 of substantially uniformcross-section to a curved J-shaped tip 12 as its distal end 14. One ormore eyes or openings 15 are also provided in the distal end 14 forpassages of fluids through the tubing 10. The proximal end of tubing 10flares outwardly for receiving various equipment such as syringes forinjecting fluids into the patient. The tapering and curvature of thetip, the flaring of the eyes and the flaring of the end are all effectedby heated tools which utilize the thermoplastic properties of theextruded tubing. This single wall tubing has a cross-section is in FIG.2 where reference numeral 30 illustrates the radiopaque composition ofthis invention.

Unlike catheters made from wholly vinyl resins, the catheter of thisexample readily resumes its shape after stretching and deforming.

EXAMPLE 17

A double wall radiopaque medical-surgical tubing is extruded in thetemperature range of 310° F. to 330° F. in a conventional manner usingconventional extrusion equipment having a biorifice tubular die forcoextrusion of an inner core and an outer shell bonded to said innertube. The tubing has an outer diameter of 0.098 inch and an innerdiameter of 0.054 inch, and the inner tube has a thickness of 0.005 inchand the outer shell has a thickness of 0.017 inch. It will be understoodthat the dimensions given are illustrative but not limiting.

Referring to FIG. 3, the thinner inner tube 18 comprises the radiopaquepolyurethane composition of Example 1.

The thicker outer wall 20 comprises the following: 65 parts ofpoly(vinyl chloride) resin plasticized with 34 parts of epoxyplasticizer, Epoxol-9-5, stabilized with 1 part of calcium zincstabilizer. This multiwall tubing is radiopaque, of low costconstruction, because of the P.V.C. heavy wall, and is especially usefulin larger sizes for stomach and nasogastric tubes. There is nopossibility for PVC or plasticizer to elute into the fluid path (shownas 19 in FIG. 3).

Similar advantages are provided when a tubing is constructed accordingto these examples, but using nylon, and polypropylene, instead of vinylin outer wall 20 of FIG. 3.

EXAMPLES 18-19

Two multiwall tubes are made by the procedure of Example 17, except thatthe inner tube 34 (FIG. 4) comprises, nylon on the one hand, andpolypropylene, on the other, and the outer shell 36 comprises theradiopaque thermoplastic polyurethane composition of Example 1. Eachtubing provides catheters with superior torque characteristics in termsof resistance to kinking when passed through tortuous body passages.

EXAMPLES 20-21

Two co-tapered multiwall tubes are made by a modification of theprocedure in Examples 18-19. The inner and outer layers are extrudedconcurrently and concentrically through annular concentric orifices of amulti-orifice extruder so as to bond the inner and outer layerstogether. The co-tapering of the inner and outer layers is obtained byvarying the rate of extrusion of the inner and outer layers. See theabovementioned Burlis et al. patent and the co-pending Flynnapplication. The rate of extrusion of the inner layer gradually variesfrom a first rate to a second rate while the rate of extrusion of theouter layer gradually varies inversely for the inner layer.

To exemplify further, reference is made to the accompanying drawing ofFIG. 6. FIG. 6 is a schematic view of a bi-orifice extrusion head 52from which tubing 40 is being extruded. Inner layer 60 is beingdischarged from the inner annular orifice of extrusion head 52. Thethermoplastic composition for inner layer 60 is delivered to theextruder head 52 by extruder 56 at a decreasing, uniform rate. The outerlayer 38 is being discharged from the concentric outer annular orificeof extruder head 52, the thermoplastic composition therefor beingsupplied by extruder 54 at an increasing rate inversely proportional tothe declining rate of extruder 56. Since the tube 40 is being drawn by aGodet (not seen in FIG. 6) the inner layer 60 is tapering downward inthickness while the outer layer 38 is tapering upward in thickness. Airline 58 provides support for the thermoplastic walls 38, 60 and assistsin defining lumen 42 during the extrusion. The increasing and decreasingrates of extrusion for inner and outer walls 60, 38 may be provided overany convenient length of time cycle to provide continuous lengths ofco-tapered, multi-wall tubing of the invention. The rates of dischargefrom extruders 54 and 56 may then be reversed to begin the taper in theopposite direction, or the original first cycle may be repeated bysynchronizing the speed of extrusion from the two extruders and thenagain increasing and decreasing the respective rates of discharge fromeach extruder 54, 56.

The co-tapered tubings are illustrated in FIG. 5 in one embodiment.

In Example 20, inner wall 60 (FIG. 5) comprises nylon and outer wall 18comprises the radiopaque thermoplastic polyurethane of Example 1.

In Example 21, inner wall 60 (FIG. 5) comprises polypropylene andouterwall 18 comprises the radiopaque thermoplastic polyurethane ofExample 1.

Surgical catheters are formed from the respective tubings of Examples 20and 21, and they exhibit a degree of flexability and softeningprogressively changing from one end to the other. Such medical-surgicalcatheters have manipulative characteristics which are advantageouslyemployed by the surgical operator in inserting, withdrawing andcontrolling the catheter.

EXAMPLE 22

A multiwall tube of co-taper construction is made following thepreceeding example where the inner core is softer than the outer jacket.This is uniquely advantageous wherein higher torque is desired.

In Example 22, softer inner core 60 (FIG. 5) comprises a 55 to 65Ddurometer thermoplastic polyurethane containing 20 parts per 100 partsby weight of composition of n-butyl 2,3,4,6-tetraiodobenzoate; andharder outerwall 18 comprises a 75D durometer thermoplastic polyurethaneand 20 parts per 100 parts by weight of composition of n-butyl2,3,4,6-tetraiodobenzoate.

EXAMPLE 23

A thin wall tubing (0.005 wall thickness) is extruded from the followingcompositions

    ______________________________________                                        Composition          Parts by weight                                          ______________________________________                                        Resin, thermoplastic polyurethane                                                                  38.04                                                    Rucothene 363                                                                 Resin, poly(vinyl chloride)                                                   BK-80 Goodyear       10.39                                                    n-Butyl 2,3,4,6-tetraiodobenzoate                                                                  18.39                                                    2-Ethoxyethyl 2,5-iodobenzoate                                                                     3.08                                                     Epoxy plasticizer, Epoxol 9-5                                                                      1.21                                                     Stabilizer CZ-11C    0.17                                                     Bismuth oxychloride  28.57                                                    ______________________________________                                    

In comparison with tubing without bismuth oxychloride, this tubing hasan enhanced tensile strength and higher radiopacity. The procedure isrepeated substituting equal parts by weight of barium sulfate per 100parts by weight of the composition for the bismuth oxychloride. Againhigher tensile strength and higher radiopacity are obtained.

Such tubings are especially useful to provide miniballoon catheters.

Obviously, the compositions of this invention provide tubings with manyadvantages. With respect to polytetrafluoroethylene catheters, thepresent invention overcomes an inability to provide a range of soft tohard catheters in a variety of wall thicknesses. This leads to areduction in mechanical trauma induced by stiffer catheters. Alsopolytetrafluoroethylene is limited in its ability to accept adequateloading of radiopaque media to be clearly visible, if a small section islost or fragmented. Furthermore, both the urethanes and theurethane-vinyls can be co-extruded according to this invention with ahard vinyl or urethane liner, which on draw down produces a thin hardknife edge impervious to peel back or fragmentation seen with thepolytetrafluoroethylene catheters.

With respect to prior art vinyl tubings, drug vehicle compatibility withthe present tubings is extended in numbers and concentration, and iodineextraction reduced, because of the ability of the urethanes andPVC-urethanes to lock in the iodo-esters. For example, they exhibit nospew or exudation when tested for four days at 100% humidity.

Obviously, many variations will suggest themselves to those skilled inthis art in light of the above, detailed description. All such obviousvariations are within the full intended scope of the appended claims.

I claim:
 1. A medical-surgical catheter formed from tubing comprising(a)a resin which includes from 100 to 33 parts by weight of a thermoplasticpolyurethane and from 0 to 67 parts of a polymer of a halogenated vinylmonomer; and (b) a radiopacifier therefor consisting of a diiodobenzoateor a tetraiodobenzoate compound of the formula ##STR2## wherein R¹ ishydrogen or iodo, and R is alkyl or alkoxyalkyl or a mixture of saidcompounds, said radiopacifier (b) comprising 10 to 40 parts by weightper 100 parts by weight of (a) and (b).
 2. A medical-surgical cathetertubing comprising (1) an interior tubular portion of a radiopaquecomposition comprising(a) a resin which includes from 100 to 33 parts byweight of a thermoplastic polyurethane and from 0 to 67 parts of apolymer of a halogenated vinyl monomer; and (b) a radiopacifier thereforconsisting of a diiodobenzoate or tetraiodobenzoate compound of theformula ##STR3## wherein R¹ is hydrogen or iodo, and R is alkyl oralkoxyalkyl and a mixture of said compunds, said radiopacifier (b)comprising 100 to 40 parts by weight per 100 parts by weight of (a) and(b),and (2) a concentric outer shell of (a) a vinyl resin as definedabove under (1) (a) and which further includes a minor proportion of aradioparent plasticizer and a minor proportion of a heat stabilizer forsaid vinyl resin; (b) nylon or (c) polypropylene.
 3. A medical-surgicalcatheter tubing as defined in claim 2 wherein, in said interior tubularportion, said resin component (a) consists of a thermoplasticpolyurethane and said radiopacifier comprises n-butyl2,3,4,6-tetraiodobenzoate.
 4. A medical-surgical catheter tubing asdefined in claim 2 wherein interior tubular portion (1) is relativelythin and outer shell portion (2) is relatively thick.
 5. Amedical-surgical catheter tubing comprising (1) an interior tubularportion of a relatively softer as measured by durometer hardnesscomposition as defined in claim 2 and (2) a concentric outer shell of arelatively harder as measured by durometer hardness composition asdefined in claim
 2. 6. A medical-surgical catheter tubing comprising (1)an interior tubing portion of nylon or polypropylene and (2) aconcentric outer shell of a radiopaque composition comprising(a) a resinwhich includes from 100 to 33 parts by weight of a thermoplasticpolyurethane and from 0 to 67 parts of a polymer of a halogenated vinylmonomer; and (b) a radiopacifier therefor consisting of a diiodobenzoateor a tetraiodobenzoate compound of the formula ##STR4## wherein R¹ ishydrogen or iodo, R is alkyl or alkoxyalkyl and a mixture of saidcompounds, said radiopacifier (b) comprising 10 to 40 parts by weightper 100 parts by weight of (a) and (b).
 7. A medical-surgical tubing asdefined in claim 6 wherein said interior tubing portion (1) comprisesnylon.
 8. A medical-surgical tubing as defined in claim 6 wherein saidinterior tubing portion (1) comprises polypropylene.
 9. Amedical-surgical tubing as defined in claim 6 having a first point alongits length and a second point along its length spaced apart from saidfirst point, the thickness of said interior tubing portion (1) taperingas it passes from said first point to said second point and thethickness of said outer shell (2) tapering inversely to the taper ofsaid interior tubing as it passes from said first point to said secondpoint.